JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. 11 May 4, 1921 No. 9 



PHYSICAL CUUMISTRY— Methods of stating acidity.' Edgap 

 T. Wherry and Eluot Q. Adams, Bureau of Chemistry. 



Both concentration and potential methods are in general use for 

 stating effective acidity and alkalinity. In the former the quantity 

 (more precisely, the concentration in gram-mols. per liter) of hy- 

 drogen ion, in the latter the logarithm of the reciprocal of this quantity, 

 are given. The concentration method is easier to understand, as is 

 brought out by table 1. 



TABLE 1 

 Comparison of Methods of Stating Acidity 



Starting at normality: Solution 1 Solution 2 



Concentration methods 



Actual number .0004 .000 0002 



Power of 10 with coefficient 0.4 X lO^^ 0.2 X 10-^ 



Power of 10 lO-'-^ 10 -«^ 



Potential method 



Ph : exponent of preceding 3.4 6.7 



Starting at neutrality: 



Potential method 



Xh: 7 - Ph 3.6 0.3 



Concentration methods 



Power of 10 lO^-e lO^-^ 



Actual number (specific acidity) 4000 2 



In this table is shown the way two values selected at random 

 appear under various methods; the first solution contains 2000 times 

 as much acid as does the second. The method used in the last line 

 obviously brings out their relative acidity with the minimum of cal- 

 culation on the part of the reader, and may be recommended to writers 

 who wish to make their data readily comprehensible. 



' Before transmitting this article for publication, it was submitted by the writers to 

 Dr. Wm. Mansfield Clark for reply or discussion, and his comments on the subject are 

 contained in the article following this one. The discussion is closed by a brief note by 

 Wherry and Adams. Received February 2, 1921. 



197 



